TECTONICS, CLIMATE, AND THE TRANSITION FROM AGGRADATION TO INCISION OF THE UPPER SANTA FE GROUP, ALBUQUERQUE BASIN, CENTRAL NEW MEXICO
CONNELL, S.D., New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, 2808 Central Ave SE, Albuquerque, NM 87106
LOVE, D.W., CATHER, S.M., New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801
SMITH, G.A., Earth & Planetary Sciences, Unvi of New Mexico, Albuquerque, NM 87131
LUCAS, S.G., New Mexico Museum of Nat History, 1801 Mountain Rd NW, Albuquerque, NM 87104
The age of uppermost Santa Fe Group sediment and onset of incision of
the modern Rio Grande Valley can only be determined by careful consideration
of the origin and distribution of unconformities in rift basins. Local
Pliocene unconformities are present along faulted basin margins, in updip
positions of tilted half-graben basin floors, and along intrabasinal faults.
In the Albuquerque basin, some of these unconformities are clearly demonstrated
to correlate to conformable stratigraphic successions within the more
rapidly subsiding parts of subbasins. Stratigraphic and geomorphic data
from the Albuquerque basin preclude the establishment of an incised Pliocene
Rio Grande, as suggested by Reneau and Dethier (1996) for the Española
basin.
The western and eastern margins of the Santo Domingo subbasin commonly
contain unconformity bounded deposits, such as the Plio-Pleistocene gravel
of Lookout Park and the Tuerto formation. Comparably aged, conformable
stratigraphic successions are exposed basinward on the hanging walls fo
the La Bajada and San Francisco faults. The Llano de Albuquerque (Calabacillas
and Belen subbasins) represents an abandoned constructional basin-floor
surface of probable late Pliocene age. Unconformities between the Arroyo
Ojito and Sierra Ladrones Fms, exposed between Tijeras Arroyo and Hell
Canyon Wash, are interpreted to be the result of local intrabasinal fautling
and a consequence of earlier incision of the ancestral Rio Puerco fluvial
system and abandonment of the Llano de Albuquerque near Albuquerque. The
youngest terminal deposits are constrained by dated tephra between 1.05-0.55
Ma and constrain the initial downcutting of the Rio Grande, probably in
response to climate change. South of White Rock Canyon, early Pleistocene
entrenchment of the Rio Grande and its major tributaries marked the termination
of widespread Santa Fe Group deposition. Smaller nonintegrated drainages,
such as those on the Llano de Manzano, continued to aggrade locally into
middle Pleistocene time. Therefore, erosional and constructional surfaces
are diachronous within and between basins and results from one locality
cannot be extrapolated throughout the rift.
Connell, S.D., Love, D.W., Cather, S.M., Smith, G.A., Lucas, S.G., 2001, Tectonics, climate, and the transition from aggradation to incision of the upper Santa Fe Group, Albuquerque basin, central New Mexico: Geological Society of America, Abstracts with Programs, Joint Rocky Mountain and Central Section Meeting, Albuquerque, New Mexico, v. 33, n. 5, p. A-48.
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